1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to a method for performing mode transition (or state transition) for a data service in a mobile station.
2. Description of the Related Art
A typical mobile communication system provides only a voice service to a subscriber. However, with the development of the communication technology and at the request of users, studies have been carried out on a mobile communication system for supporting not only the voice service but also a high-speed data service for image communication and the Internet. A CDMA2000 (Code Division Multiple Access 2000) 1xEV-DV (Evolution in Data and Voice) mobile communication system supporting both the voice service and the data service includes a base station (BS) servicing a mobile station (MS), a subscriber terminal. The base station commonly separates circuit channels for the voice service and packet channels for the data service, and assigns, to the packet channels, the remaining radio resources except the radio resources used for the circuit (voice) channels. Here, the “radio resources” used in the base station include transmission power, the number of Walsh codes, and time periods (or time slots).
In the CDMA2000 1xEV-DV system, a forward packet data channel (F-PDCH) for a data service, transmitted from BS to MS, has data transmission periods and data non-transmission periods, which may irregularly occur due to a bust traffic characteristic of the data service. Therefore, the mobile station and the base station generally make a transition to a control hold mode (CHM) in the data non-transmission period, and then make a transition to an active mode (AM) if there is data to transmit. In the control hold mode, reverse channels and forward channels undergo gated transmission (or intermittent transmission). The gated transmission is one of the techniques proposed to save radio resources of the base station and minimize power consumption of the mobile station.
FIG. 1 is a message flow diagram illustrating an exemplary mode transition operation of a mobile station according to the background art. In FIG. 1, a forward common assignment channel (F-CACH) is assigned between a mobile station (MS) and a base station (BS), and monitored by the mobile station to make a transition from a control hold mode to an active mode. The base station transmits RAM (Resource Allocation Message) or RAMM (Resource Allocation Mini Message) over the F-CACH. The RAM or RAMM serves as a mode transition instruction message for instructing mode transition from the control hold mode to the active mode.
Referring to FIG. 1, the mobile station in the control hold mode continuously monitors the F-CACH while intermittently transmitting a reverse pilot signal and a reverse channel quality indicator over reverse channels R-PICH and R-CQICH to the base station. At this point, a forward fundamental channel (F-FCH) or a forward dedicated control channel (F-DCCH) for the data service is not assigned. Further, the base station in the control hold mode intermittently transmits PCB (Power Control Bit), information for forward power control, over a forward common power control channel (F-CPCCH). Here, “intermittent transmission (or gated transmission)” means that information is non-continuously exchanged between the base station and the mobile station at a predetermined gating rate. The gating rate is determined based on control messages exchanged between the base station and the mobile station before data communication is performed.
If there is data to transmit to the mobile station, the base station transmits RAM or RAMM with MAC_ID (Medium Access Control Identification), a unique ID of the corresponding mobile station, over the F-CACH, and then transmits an encoder packet (EP) size and a slot length of packet data to be transmitted, over F-SPDCCH/F-PPDCCH (Forward Secondary Packet Data Control Channel)/(Forward Primary Packet Data Control Channel). Thereafter, the base station transitions to the active mode and transmits data over F-PDCH. Upon receiving the RAM or RAMM with its MAC_ID from the base station over the F-CACH, the mobile station acquires the encoder packet size and slot length of the packet data by monitoring the F-SPDCCH/F-PPDCCH. Thereafter, the mobile station transitions to the active mode and decodes the data received over the F-PDCH. In the active mode, all gated information (reverse pilot signal, reverse channel quality indicator information, and PCB) are transmitted at a full rate.
However, in the conventional mode transition method of FIG. 1, the dedicated F-CACH must be allocated between the base station and the mobile station and continuously monitored by the mobile station, causing an increase in power consumption of the mobile station.
FIG. 2 is a message flow diagram illustrating another exemplary mode transition operation of a mobile station according to the background art. Referring to FIG. 2, in the control hold mode, only the F-SPDCCH/F-PPDCCH and not the dedicated F-CACH are allocated between the mobile station and the base station. In the same way as described in conjunction with FIG. 1, the mobile station in the control hold mode intermittently transmits a reverse pilot signal and a reverse channel quality indicator. However, contrary to FIG. 1, the base station in the control hold mode transmits the F-SPDCCH at a full rate, and the mobile station continuously monitors the F-SPDCCH.
If there is data to transmit to the mobile station, the base station transmits MAC_ID of the mobile station over the F-SPDCCH. Thereafter, the base station transitions to the active mode and then transmits data over the F-PDCH. Upon receiving its MAC_ID on the F-SPDCCH, the mobile station transitions to the active mode and then decodes data received over the F-PDCH to transmit HARQ(Hybrid Automatic Repeat request) ACK/NACK in response to the decoded data. The mobile station in the active mode transmits a reverse pilot and a reverse channel quality indicator at a full rate.
FIG. 3 is a flowchart illustrating an operation of making a transition from a control hold mode to an active mode by a mobile station in accordance with the message flow of FIG. 2. Referring to FIG. 3, in step 300, a mobile station in a control hold mode continuously monitors F-SPDCCH. In step 305, the mobile station decodes the F-SPDCCH and determines whether its own MAC_ID is detected from the F-SPDCCH. Upon failure to detect its MAC_ID, the mobile station returns to step 300. Otherwise, upon detecting its MAC_ID in step 305, the mobile station transitions, in step 310, to an active mode and starts receiving F-PDCH from a base station and transmits HARQ ACK/NACK in response to the received data. In step 315, the mobile station transmits R-PICH (Reverse Pilot Channel) and R-CQICH (Reverse Channel Quality Indicator Channel) at a full rate.
FIG. 4 is a flowchart illustrating an operation of making a transition from a control hold mode to an active mode by a base station in accordance with the message flow of FIG. 2. Referring to FIG. 4, if there is data to transmit to a mobile station, a base station in a control hold mode transmits MAC_ID of the corresponding mobile station over F-SPDCCH in step 400. Thereafter, in step 405, the base station transitions to an active mode and then starts transmitting packet data over F-PDCH. Subsequently, the base station transmits F-CPCCH (Forward Common Power Control Channel) at a full rate, in step 410. At this moment, PCB transmitted over the F-CPCCH is determined based on information intermittently received over R-PICH and R-CQICH for a reverse link.
However, even in the mode transition method described in conjunction with FIGS. 2 to 4, the mobile station must continuously monitor F-SPDCCH or F-PPDCCH in the control hold mode without perceiving presence of a mode transition message, thus causing an increase in power consumption of the mobile station.